A touch panel as one type of a planar device having a line placed along a plane is to detect a touch for example with a finger to specify the coordinates of the position of the touch. The touch panel has gained attention as one of excellent user interfaces. The touch panel which is currently commercially available includes various types of touch panels including a resistive touch panel and a capacitive touch panel. The touch panel is generally formed of a touch screen including a built-in touch sensor and a detector that specifies the coordinates of a touched position based on a signal from the touch screen.
A projected capacitive touch panel is one type of the capacitive touch panel (see Japanese Patent Application Laid-Open No. 2012-103761, for example). The projected capacitive touch panel allows detection of a touch, even if a front surface of a touch screen with a built-in touch sensor is covered with a protection plate such as a glass plate of a thickness of several millimeters. The touch panel of this system has excellent robustness as it allows installation of the protection plate on the front surface. Additionally, the touch panel of this system allows detection of a touch even with a gloved finger. Further, the touch panel of this system has a long life as it does not have a movable part to be deformed mechanically.
For example, the projected capacitive touch panel includes the following elements as detector lines for detecting a capacitance: a first series of conducting elements formed on a thin dielectric film and a second series of conducting elements formed over the first series of conducting elements with intervention of an insulating film. Each conducting element is not electrically connected to a different conducting element. These conducting elements cross each other three-dimensionally at several points. A capacitance formed between an indicator such as a finger and each of the first series of conducting elements and the second series of conducting elements is detected using a detector circuit, thereby specifying the coordinates of a position touched with the finger. This detection system is generally called a self capacitance detection system (see Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 9-511086 (1997), for example).
According to another example of the detection system of specifying the coordinates of a touched position, change in an electric field between a plurality of row-direction lines extending in a row direction and a plurality of column-direction lines extending in a column direction, specifically, change in a mutual capacitance is detected. This detection system is generally called a mutual capacitance detection system (see Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-526831, for example).
In either structure of the aforementioned self capacitance system and mutual capacitance system, in the presence of a touch with an indicator such as a finger in one of planar regions (detector cells) in a lattice pattern formed by partitioning using the row-direction lines and the column-direction lines, the position coordinates of the touch are generally specified by a method using a balance between a value detected in a sensor block and a value detected by a detector cell near the sensor block.
Forming a mesh wire made of low-resistance metal instead of a transparent conductive film made of a material such as indium tin oxide (ITO) has recently been suggested as a technique of increasing detection speed or increasing the size of a touch screen (see Japanese Patent No. 4869309, for example).
A display device, as a different type of the planar device having a line placed along a plane, has been used to realize reduction in power consumption and reduction in the thickness of the device. One example of this display device includes an active matrix thin film transistor (hereinafter called a “TFT”) used as a switching element. Such a display device has been required to achieve further reduction in resistance of a lead-out line, etc. in response to larger size, higher rate, or higher definition of a screen.
However, even if a sensor line (detector line) is formed by using a mesh wire made of low-resistance metal as in Japanese Patent No. 4869309, increasing the size of a touch screen still increases the length of a lead-out line extending from a signal input terminal part of the touch screen to the detector line, particularly the length of the lead-out line in an external area. This increases wiring resistance of the lead-out line in this area. Increase in the resistance of the lead-out line increases the probability of the occurrence of breakdown in an insulating film forming the sensor line due to electrostatic discharge (ESD), causing a problem in that touch function might be lost easily.
In a display device, increase in the size of a TFT substrate on which a TFT is formed also increases resistance of an external lead-out line. This increases the probability of the occurrence of breakdown in an insulating film between a gate line and a source line connected to this lead-out line, causing a problem in that a line defect might be caused easily on the display device.